Analysis of common lithium salts, trace additives, and contaminants in lithium-ion battery electrolytes by ion chromatography-mass spectrometry

Importance of the Topic

The precise characterization of lithium-ion battery (LIB) electrolytes is critical for optimizing cell performance, extending cycle life, and ensuring safety across research, production, and recycling workflows. Trace contaminants or additive degradation products can undermine efficiency and accelerate aging, making sensitive, high-throughput analysis of both common lithium salts and minor byproducts indispensable.

Study Objectives and Overview

This work introduces a combined ion chromatography–mass spectrometry (IC-MS) method to quantify 15 key anionic species—ranging from simple fluorides and acetates to complex bis(trifluoromethanesulfonimide) salts—in simulated LIB electrolytes. By coupling suppressed conductivity detection with selective ion monitoring (SIM) on a single-quadrupole MS, the approach aims to deliver rapid, accurate profiling of salts, additives, and hydrolysis products in under 40 minutes per run.

Methodology and Instrumentation

Sample Preparation:

• Simulated electrolyte matrix: equal-weight mixture of ethylene carbonate, dimethyl carbonate, and diethyl carbonate.
• Dissolution of lithium salts at defined concentrations; 100× dilution in deionized water; 0.45 µm filtration.

Chromatographic Conditions:

• System: Thermo Scientific Dionex ICS-6000 HPIC.
• Column: Dionex IonPac AS23 analytical (2 × 250 mm) with AG23 guard (2 × 50 mm).
• Eluent A: 45 mM Na₂CO₃ + 25 mM NaHCO₃; B: DI water; C: acetonitrile gradient to accelerate elution.
• Flow: 0.25 mL/min; column temperature: 40 °C; injection: 5 µL full loop.
• Suppressor: ADRS-600 dynamically regenerated (10 mA, recycling/external water mode); CRD-300 carbonate removal in vacuum mode.

Mass Spectrometry:

• Instrument: Thermo Scientific ISQ EC single-quadrupole MS, ESI negative mode.
• SIM m/z channels set for each analyte; ion transfer tube at 350 °C; vaporizer at 500 °C.
• Diverter valve logic programmed in Chromeleon CDS to protect MS from high-salt fractions.

Instrumentation Used

• Dionex ICS-6000 HPIC system with DP gradient dual pump and AXP-MS pump.
• Thermo Scientific Dionex AS-AP autosampler and DC conductivity detector.
• Dionex IonPac AG23 guard and AS23 analytical columns.
• Dionex ADRS-600 suppressor and CRD-300 carbonate removal device.
• ISQ EC single-quadrupole mass spectrometer.
• Chromeleon CDS Software 7.3.2 or higher.
• Reagents: sodium carbonate, bicarbonate, acetonitrile, LiPF₆, LiBOB, LiTFSI, LiFSI, LiBF₄, LiODFB, LiPO₂F₂, plus standard anions.

Main Results and Discussion

Separation of all 15 analytes was achieved in a single 45-minute gradient with baseline resolution under conductivity and MS-SIM detection. Calibration curves exhibited excellent linearity (r² ≥ 0.996) over broad ranges. Limits of detection and quantitation spanned 0.02–72 µg/L (LOD) and 0.07–221 µg/L (LOQ) depending on the analyte.

Simulated electrolyte spike recoveries ranged from 60 % to 142 %, with elevated fluoride and fluorophosphate signals indicating partial hydrolysis of precursors. A sequence of 55 injections demonstrated retention time RSDs below 0.5 % and peak area RSDs typically under 10 % for major components, confirming method robustness.

Hydrolysis studies highlighted degradation pathways of PO₂F₂⁻ to PO₃F²⁻ and fluoride under high-pH conditions. The use of carbonate/bicarbonate eluents minimized in-cell salt decomposition compared to KOH, while a programmable diverter valve preserved MS integrity.

Benefits and Practical Applications of the Method

• Simultaneous quantitation of common salts, additives, and trace contaminants in LIB electrolytes.
• Dual detection (conductivity and MS-SIM) enhances selectivity, sensitivity, and confirmation capability.
• Short analysis time (<40 min) and high throughput suited for R&D, quality control, and failure analysis.
• Automated diverter valve integration reduces instrument downtime and maintenance.

Future Trends and Opportunities

Advances may include in-line IC-MS monitoring for real-time process control in battery manufacturing and recycling. Further optimization of eluent chemistries and column materials could reduce hydrolysis artifacts. Integration with machine-learning algorithms for chromatogram interpretation and expansion to next-generation battery chemistries (e.g., sodium-ion, solid-state) represent promising directions.

Conclusion

The presented IC-MS method offers a comprehensive, robust platform for profiling lithium-ion battery electrolytes. By combining suppressed conductivity detection with targeted MS-SIM in a single run, it enables accurate quantitation of a broad span of salts, additives, and degradation products—supporting continued innovation and quality assurance in LIB development.

References

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